Controlling- phase relations between stations



Dec. 24, 1929. H. NYQUIST 1,740,620

CONTROLLING PHASE RELATIONS BETWEEN STATIONS Filed 001', l9, 1927 2 Sheets-Sheet 1 F limited limes s/wgu art eZectrq-Statne lat um uerlwcalp me.

\ \e /gl I s J 1 A m we /m' n H X. 1 T .c & a a

firmer/ma :5 Zeceab I N V Ely TOR. .E @qw BY A TTORNEY Dec. 24, 1929. H. NYQUIST CONTROLLING PHASE RELATIONS BETWEEN STATIONS Filed Oct. 19, 1927 2 sheet's -sheet 2 Jfaynetz'c Field *Wst 1 00 Mem 2 loc ted at vith each other.

Patented Dec. 24, 1929 UE'E'D 3T ljledtzd Par HARRY NYQ'UIST, OF MILLB'URN, NEVZ JERSEY, ASSIGNOR TO AMERICAN TELEPHQNE AND TELEGRAPH COMPANY, A GORPGRATION 033 NEW YORK CONTROLLING PHASE RELATIONS BETWEEN STATIONS Application filed October 19, 1.927.

This invention relates to methods and arrangements for maintaining thecurrent supplied from one station over a line to a distant station in a desired phase relation. More particularly, the invention has application to maintaining constant phase relations between the carrier waves of plurality of broadcasting stations transmitting upon the same wave length.

When distant ranio stations are connected by telephone lines so that they may broadcast the same program, it becomes desirable that all the stations use the same carrier frequency in order to red ce'the number of wave lengths required for the one program. Such a method of operation, however, encounters the difficulty that slight-changes in the relative phases of the radio frequency currents from the various broadcasting stations atiect the field strength in certain localities, thus causing received signals to vary in amplitude, and in some cases to vanish completely.

In accordance with the present invention, it is proposed to remedy this condition by supplying a controlling current of some base frequency over wire lines to the various broadng stations, the common carrier wave at the various broadcasting stations being derived from or controlled by the base frequency so transmitted. in order to compensate for the variation in phase produced upon the controlling or base frequency by reason of temperature or other variations of the line, a special automatic arrangement is provided to produce in the line changes to compensate for the changes in phase.

Specifically, the present invention comtem- -cs controlling the phase variation by pie ing up waves from two radio transmitters interconnected by a telephone line over which a controlling frequency is transmitted, said vaves being picked up at two points in the immediate vicinity of and equidistant from a third point so located between the two transmitters that under normal phase conditions the waves from the two transmitters will an nul each other, thereat. The waves thus picked up are then combined to produce a null eii'eet r the two transmitters are in phase If, however, the two trans- Serial No. 227,304.

mitters are out of phase, the waves picked up at the two pick-up points will not produce a null effect, and this fact is taken advantage of to automatically operate the phase adjusting network in the line over which the controlling frequency is transmitted to compensate for the variation in phase indicated.

T he invention may now be more fully unde stood from the following detailed description thereof when read in connection with the accompanying drawing, of which Figure 1 shows curves illustrating the principles underlying the invention; Figs. 2 and 3 illustrate schematically certain types of radio antennae; 4 shows curves indicating the distribution of magnetic field strength under different phase conditions atpoints intermediate between two broadcasting transmitters; 5 illustrates a circuit arrangement embodying one form of the invention; and 6 shows with some degree of detail the control mechanism symbolically represented in Fig. 5.

As a simple illustration of varying field strength let us consider two broadcasting stations symbolically represented at the points designated east and west in Fig. 1. Each station may be supposed to have a similar antenna consisting of a vertical rod with equal sources ofelectromotive force between the rod and the ground. Under these circumstances, antenna is surrounded by a magnetic field and an elect ic field, these fields decreasing in strength with increasing distance from the antenna. Only a few lines of force are shown in the diagram of Fig. l in orderto indicate the direction of certain portions of the fields. V The lines marked 6 and e represent lines of force of the electric field, the arrows indicating the direction. Similarly, the circles marked m and m indicate the lines of force of the magnetic lielchentering and leaving the paper in a plane at right angles thereto. The circles with the crosses represent positive lines of force and the circles with the dots in the center represent negative lines of force.

If the currents in the several-antennae are in phase, then at the point a midway between the stations the magnetic flux m surrounding 9 and 9 are phase angle constants. the first term of the quantity represented by the right hand side of the equation is the current due to the magnetic field, while the second term is that due to the electric field.

The current flowing in .the receiving antenna due to waves from the west station may be represented:

I F A cos (wt I )+A cos (wt W (2) wave length distant from a, the fluxes would substract. At 0, one-half wave length from a, the fluxes would again add. The same holds true approximately for locations within a short distance northor south of these points.

On the other hand, the individual electric in which A and A are again magnitude constants, which may have the same or nearly the same values as in the case of Equation (1), and I and Q are phase angle constants.

These expressions may be rewritten in the form of resultant vectors, as follows:

i V241 +142 214. 11 COS (I 2 l COS 3 fields c and e are a maximumwhen the mag netic fields m and m are a maximum. Due

to their relative directions at point a, however,

the resultant of 6 plus 6 is a maximumwhile that of m plus m is zero. As phase shifts occur, the location of maximum and minimum resultantelectrostatic fields is changed.

It is, of course possible to devise receiving antennae structure which will respond to the magnetic fields Without being substantially affected by the electric fields,.and vice versa. For example, the loop type antenna such as is illustrated schematically in Fig. 2, responds mainly to magnetic fields, while' the antenna of the type conventionally indicated in Fig. 3 responds mainly to electric fields. The majority of antennae, however, such as L or T type antennae, are responsive to both mag netic and electric fields.

lVith these considerations in mind, let us analyze the character of the current received where the antenna is responsive to both mag i v Where n is any odd number. It follows, therefore, that at points approximately midway netic and electric fields and located at any given point in the vicinity of a of Fig. 1.

I Assuming the point a lies midway'between two similar transmitters, each transmitting through similar media, let a" equalthe distance from the point-a to a receiving station near a and located on the line ca of Fig. 1. Also, let A equal the wave length of both oscillators. Then the current fiowingin' the re ceiving antenna due to waves from the east transmitter is: r

In Equations (3) and l), the symbols 9 and I' havethe following values:

6 t n A1 Sin 91+A2 Sin 92 3 a A cos 6 +11 cos 9 A sin I +A sin I 1%1A 1,3 tan A cos I +11 cos 1' (6) Now, since the phase angle constants in the foregoing equations are fLlIlCtlOIlS of the transmittin antennae and the transmittin media, which are assumed to be the same for both transmission east and west, it is evident that the expressions cos (6 9 and cos (ri -1 in Equations (3) and (4) will be equal to each other, and hence the terms under the radicals'in said equations are equal. It is also evident that I plus 1 add up to zero 7 whenever I' 6 i mradians.

is provided at each station by means of har monic generators of radio frequency driven In the foregoing equation, t is the time of transmlssion; his 271- times the frequency; A and A are magnitude constants; and

or controlled by the same fundamental controlling current (preferably of voice frequency) transmitted over a telephone line Also, I

, A is so plotted that its ordinates show the amplitude of the magnetic field component along the line a-bc located approximately midway between the two radio broadcasting stations considered in connection with Fig.

a 1. Curve A shows that the points of maximum field strength are approximately onehalf wave length apart. This is evident from a consideration of Equations and (2) above given, which show that the portion of the antenna current due to the resultant magnetic fields is proportional to cos (wt- 9 cos (ww l h as 27-113 cos I cos SlIl I s1n sin? cosI cos i sinil lsin wt Now, bearing in mind that in Equations (1) and (2) represents the distance from the midpoint between the two transmitters to any assumed pick-up or receiving point, it becomes evident that if we let an equal zero in the final expression for M given by Equation (8), we will then have the value of the magnetic field at the point a of Figs. 1 and 4, which is:

M (cos 9 cos 1 cos wt" (sin 6 sin I sin wt So, also, if we let an equal 2 in equation (8),

we obtain the value of the magnetic field at the point 6 of Fig. 4, which is:

M (sin 9 sin I cos wt-I- (cos 9 cos I sin wt Now, if we assume that the phase angle constants 6 and Q are both multiples of 271', then cos wt 2 s1n cos 9 cos em 9 sin wt Equations (9) and (10) reduce to:

M =2 cos wt (11) As Equation (11) is the expression for the maximum value of the field strength, whereas Equation (12) represents the minimum condition, it is evident that the field strength varies from zero to a maximum value within the distance of a quarter wave length, and that hence the points of maximum field strength are approximately one-half wave length apart, as previously stated.

The curve B of Fig. 4 shows the amplitude of the magnetic field at points along the same line (a7)c) after the relative phase between the two transmitting stations has shifted a fraction of a period P. The distance which the curve A would have to be dis 2 to a phase shift of 180. Then the curve A would be shifted 2 so that Wherever a max- .two stations be maintained substantially constant. This result may be accomplished b the arran ement shown 111 F1 5. Here b g two radio transmitting stations, RT and RT are conventionally indicated, these radio stations being interconnected by a telephone line L over which a base or controlling frequency, supplied by a source S, may be transmitted. At each radio transmitter it is understood that the conventional symbol will include suitable means by which the common carrier wave employed at the two stations may be derived from or controlled by the frequency transmitted over the line L. This may be accomplished, for example, by the use of harmonic generators of a well-known type. The line L includes, at some point near the middle thereof, a phase shifting network PN, by the adjustment of which the phase of the controlling current transmitted over the line L may be maintained the same 'at the station RT" as at the station RT. When this condition occurs, it follows that the derived carrier waves will also be in phase at both stations.

In order to automatically control the phase shifter PN, loop antennae 1 and 2 are located at points such as cl and e of Fig. 4, these points being equidistant from and on either side of a point at which, under normal conditions, the magnetic components of the wave from the two transmitters will neutralize each other. The voltages induced in these antennae will be equal since the ordinates cZf in Fig. 4 are equal to the ordinates eg. It is also evident that a slight change of phase P will cause unequal voltages to be induced in the two antennae, as is indicated by the fact that the ordinates eh in Fig. 4: are greater than the ordinates cZ/c, when the curve is shifted to the position represented by the curve B.

Each antenna is connected to receiving sets R and R conventionally indicated in the diagram of Fig. 5. These receiving sets may be of any type well known in the art and function to translate the received waves picked up by the two antennae into voice frequency currents, which may be transmitted over short lines L and L of equal length, to a common point adjacent the line L.

The currents transmitted over the lines L and L are then passed through transformers 3 and 4 to a detector arrangement comprising two vacuum tubes 5 and 6, which are connected to a polar relay PR, said polar relay operating a control mechanism symbolically indicated in the diagram of Fig. 5 but lllustrated in somewhat more detail in Fig. 6.

If we assume that the voltages in the antennae 1 and 2 are equal, then the radioreceiving sets R and It: and the lines L and L will be adjusted so that the current I flowing in the upper winding of the polar relay PR will be ust equal to the current I flowing in the lower winding thereof. Under these conditions, the relay armature will be in neutral position. Should the voltages induced in tlie'antennae become unequal, due to a phase shift P in waves-radiated from the two transmitters, as explained above, the resulting inequality in the currents, I and I would operate the armature of the polar relay in one direction or the other, depending upon the direction of the phase shift.

Referrin to Fig. 6, if the armature of the relay PIQ be shifted to its upper position the relay 7 will be energized to cause the motor M to rotate in one direction. If the armature of the relay is shiftedto its lower contact the relay 8 becomes energized and causes the motor M to rotate in the opposite direction. The shaft of the motor M may be geared in any suitable manner to adjust the phase shifting network PN until the two transmitting stations are again brought into synchronism, when the armature of the relay PR will again be in neutral position. 7 In this manner, the condition of synchronism between the two stations is automatically maintained.

It will be understood that the controlling mechanism specifically illustrated in Fig. 6 is merely disclosed for purposes of illustration, it being obvious that any other known form of controlling mechanism may be employed. Likewise, the phase shifting network PN is merelv indicated symbolically, it being understood that any well-known type of phase shifter may be automatically adjusted by suitable control mechanism.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

1. In a system in which a plurality of radio transmitters operating upon a common wave length are interconnected by a wire line including a phase controlling element, said line transmitting a fundamental controlling frequency to determine the radio wave length employed; the method of maintaning a constant phase relation between any two stations so interconnected, which consists in picking up waves at two pick-up points close to but equidistant from a nodal point at which the combined waves fromthe two stations will substantially annul each other under normal phase conditions, combining said waves to produce a null effect under normal phase conditions and to produce an effect determined by phase variation under abnormal conditions, and adjusting the phase controlling element of the interconnecting line to compensate for the indicated phase variation.

'2. In a system in which a plurality of radio transmitters operating upon a common wave length are interconnected by a wire line including a phase controlling element, said line transmitting a fundamental controlling frequency to determine the radio wave length employed; the method of maintaining a constant phase relation between any two stations so interconnected, which consists in picking up waves at two pick-up points close 'tobut equidistant from a nodal point at which the combined waves from the two stations will i substantially annul each other under normal phase conditions, transmitting the waves icked up over similar circuits to a common point, combining the Waves at said common point to produce a null effect under normal phase conditions and to produce an effect determined by phase variation under abnormal conditions, and automatically controlling the adjustment of the phase controlling element of the interconnecting line to compensate for the indicated phase variation.

3. A system including a plurality of radio transmitters operating upon a common wave length, a wlre line lnterconnecting a palr of said transmitters, means to transmit a fundamental controlling frequency over said wire line, means at each transmitter to determine from said frequency the wave length employed by the transmitters, means to pick up waves from said transmitters at two pickup points close to but equidistant from a nodal point at which combined waves from the two stations will substantially annul each other, means to combine said waves to produce a null effect under normal phase conditions and to produce an eiiect determined by phase variation under abnormal conditions,and a phase October, 1927.

HARRY NYQUIST.

controlling element for the interconnecting P line adjustable to compensate for the inclicated phase variation.

4. A system including a plurality of radio transmitters operating upon a common wave length, a wire line interconnecting a pair of said transmitters, means to transmit a fundamental controlling frequency over said wire line, means at each transmitter to determine from said frequency the wave length employed by the transmitters, means to pick up waves from said transmitters at two pick-up points close to but equidistant from a nodal point at which combined waves from the two stations will substantially annul each other, electrically similar circuits for transmitting the waves picked up at the two pick-up points to a common point, means at said common point to combine the waves to produce a null efiect under normal phase conditions and to produce an effect determined by phase variation under abnormal conditions, and a phase controlling element for the interconnecting line adjustable to compensate for the indicated phase variation.

5. A system including a plurality of radio transmitters operating upon a common wave length, a wire line interconnecting a pair of said transmitters, means to transmit a fundamental controlling frequency over said wire line, means at each transmitter to determine from said frequency the wave length employed by the transmitters, means to pick up waves from said transmitters at two pickup points close to but equidistant from a nodal point at which combined waves from the two stations will substantially annul each other, electrically similar circuits for transmitting 

